Contact: Kate Kuykendall, 805-370-2343LOS ANGELES - A paper published today in the Proceedings of the Royal Society B found that mountain lions in the Santa Monica Mountains face the possibility of extinction in the near future. Using detailed demographic and genetic information from a long-term study of the population by the National Park Service, researchers from NPS, UCLA, UC Davis, and Utah State University developed a population viability model to evaluate how likely the local population is to persist under a variety of scenarios.
The good news is that the population is currently vigorous, with stable population growth and healthy rates of survival and reproduction. However, because the population is isolated from surrounding natural areas by major freeways and development, the viability model predicted a rapid decline in genetic diversity over the next 50 years. Such a decline could result in the population going extinct if the lack of genetic diversity begins to negatively affect the ability of mountain lions to survive and reproduce –a phenomenon known as inbreeding depression.
"The Santa Monica Mountains population, along with the one in the Santa Ana Mountains in Orange County, has the lowest genetic diversity documented for mountain lions aside from Florida panthers," said lead author Dr. John Benson, a wildlife ecologist with the La Kretz Center for California Conservation Science at UCLA, who also spent time studying the panther population (despite the different common names, panthers and mountain lions are the same species). "So we can look to what happened to Florida panthers as a cautionary tale. When their genetic diversity reached very low levels in the 1990s, panthers nearly went extinct due to factors associated with inbreeding depression."
If inbreeding depression occurs in the Santa Monica Mountains population, the model predicted a 99.7% chance of extinction within 50 years, with a median time to extinction of just 15 years. However, there is reason for hope: the researchers modeled the population with different numbers of new mountain lions entering the population, and even a modest increase in immigration to one animal every two to four years should maintain current levels of genetic diversity. A solution to address this issue -- a wildlife crossing across the 101 Freeway, the biggest barrier between the Santa Monica Mountains and other large natural areas -- is currently being drafted by Caltrans. A private fundraising initiative, Save LA Cougars, is raising money for the effort. If a wildlife crossing was built across the freeway, it would allow for mountain lions living north of the Santa Monica Mountains to travel into the range.
In 2009, subadult male P-12 successfully crossed the 101 from the Simi Hills, the only documented crossing from north to south during the study. When he subsequently became a breeding adult, the introduction of his genetic material had a positive, but short-lived effect on the population's genetic diversity. Since then, he has mated with two of his immediate offspring and a granddaughter, examples of very close inbreeding which further eroded genetic diversity in the population.
In the past, more general theoretical models have predicted that about one successful migrant per generation would be sufficient to maintain genetic diversity in isolated populations, and this study supported that hypothesis with data from a real population. The increase in connectivity provided by a wildlife crossing would also benefit the population by allowing young animals born in the Santa Monicas to disperse elsewhere, thus reducing the likelihood of close relatives mating. Most importantly, a north-south connection for wildlife across the freeway would also benefit all the other species whose movements are blocked by this massive barrier. Previous National Park Service and UCLA studies have found genetic differentiation as a result of urban development and roads for other carnivores such as bobcats and coyotes, but also for smaller, more abundant species such as western fence lizards, and even for a bird, the wrentit.
Because of its very small size, the Santa Monica Mountains mountain lion population is at significant risk of extinction even before inbreeding depression sets in: the model found a 15-22% chance of extinction over the next 50 years just from the variation in breeding and mortality from year to year. Generally just one or two adult males have dominated breeding in this population. This means that if in one week one of the males dies from a fight with another mountain lion, and the other dies from being hit by a car or from rat poisons, two common causes of mortality in the Santa Monica Mountains, breeding within this population could quickly come to a halt and greatly increase risk of extinction. Once again, increased immigration provides an answer -- with just one immigrant every two years, the extinction probability predicted by the model was an order of magnitude lower, at 2.4%.
"Fifty-plus years ago when the 101 Freeway was built, no one was thinking about wildlife connectivity," noted Dr. Seth Riley, a wildlife ecologist for the National Park Service, associate adjunct professor at UCLA, and senior author of the study. "We have worked for years with our partners to increase connectivity across the 101 for all animals, but this study really drives home how serious the threat is for mountain lions, the species most at risk of being lost."
Population viability models have been used in the conservation field since its inception as an academic discipline 40 years ago, and the importance of demographic versus genetic factors has long been argued. In more recent years, detailed genetic data has become available for wildlife populations, however few studies have realistically integrated genetic and demographic data into the same models. The result from the Santa Monica Mountains model, that genetic factors can also have a major impact on extinction risk, is an important one. Similar modeling efforts that explicitly consider interactions between demography and genetics could be valuable for other small, well-studied wildlife populations of conservation concern around the globe.
Mountain lions are large carnivores that can weigh up to 150 pounds in California. Males use ranges of up to 200 square miles, although in Southern California, roads and development can limit movement.
Since 1996, the National Park Service has been studying carnivores in and around the Santa Monica Mountains to determine how they survive in an increasingly fragmented and urbanized environment. During the course of the study, biologists have studied more than 340 bobcats, 145 coyotes, and 50 mountain lions.
Santa Monica Mountains National Recreation Area (SMMNRA) is the largest urban national park in the country, encompassing more than 150,000 acres of mountains and coastline in Ventura and Los Angeles counties. A unit of the National Park System, it comprises a seamless network of local, state, and federal parks interwoven with private lands and communities. As one of only five Mediterranean ecosystems in the world, SMMNRA preserves the rich biological diversity of more than 450 animal species and 26 distinct plant communities.
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Last updated: November 1, 2018